It is frequently necessary to hold fixtures such as shelves, pipes, heating ducts, rows of seats, machinery and the like, which are hereinafter referred to as fixtures, to concrete, brick, stone, plaster, stucco, plasterboard or the like, which are hereafter referred to as concrete. Many anchor systems have been used for this purpose. The most primitive anchors are wooden plugs driven into holes drilled in concrete to anchor fixtures with ordinary wood screws. Other systems use deformable metal such as lead which can receive a screw and which can be deformed to provide a high-friction bond with a hole drilled into concrete.
More recently adhesive has been used to hold anchor members such as threaded studs in holes. Adhesive, which will hereinafter be called epoxy, is very effective because fixing a stud and attaching it to the fixture can be done in a single operation. For example, installing a row of stadium seats on a concrete platform can be accomplished by placing the seats where they are ultimately to be attached, drilling holes in the concrete through the holes in the feet of the seats that are provided for holding them and, after cleaning dust from the holes, partly filling the holes with epoxy and afterwards putting a seat-holding stud in each hole. When the epoxy sets it bonds the stud firmly to the concrete with a bond that is permanent, waterproof and usually stronger than the concrete to which it is bonded. However, studs anchored in that way cannot easily be removed. Accordingly, fixtures held with adhesive bonding as described above normally are held with threaded studs instead of bolts so that fixtures can be removed by removing a nut from the threaded portion of the stud that extends out of the hole in the concrete. Typical of such studs are those known as EPCON ANCHORS sold by ITW RAMSET/REDHEAD of Wood Dale, Ill.
More recently, studs set in concrete with epoxy have been first coated with a release for the epoxy--typically TEFLON tape wrapped around the threads that are set in an epoxy bond so that the set epoxy in the hole acts more as a nut than as a permanent bond. TEFLON is a trademark for polytetrafluoroethylene materials. In such uses a threaded stud can be screwed out of the epoxy because the release material prevents bonding of the epoxy to the metal. A problem with anchors of that nature is that, although the stud can be removed from the epoxy plug by screwing it out, it cannot be screwed any farther into the hole because epoxy surrounds the bottom of the stud as well as its sides. Thus, if it is desired to screw a bolt or a threaded stud farther into an epoxy-bonded anchor, it is necessary to remove that threaded member and to replace it with a shorter one that will not reach the bottom of the threaded epoxy cavity. This limitation has virtually mandated that anchors set in epoxy be threaded studs which permit tightening the connection to a fixture by tightening an external nut on that part of the stud that extends out of the hole in which it is bonded.